Naphthenic acid corrosion inhibition using new synergetic combination of phosphorus compounds

ABSTRACT

The present invention relates to the field of processing hydrocarbons which causes corrosion in the metal surfaces of processing units. The invention addresses the technical problem of high temperature naphthenic acid corrosion and sulphur corrosion and provides a solution to inhibit these types of corrosion. The three combination compositions are formed by three mixtures separately, with one mixture obtained by mixing compound A, which is obtained by reacting high reactive polyisobutylene (HRPIB) with phosphorous pentasulphide in presence of catalytic amount of sulphur with compound B such as trialkyl phosphate and second mixture obtained by mixing compound A with compound C such as phosphite like di-isodecyl phenyl phosphite, and third mixture obtained by mixing compound A with compound D such as a phosphonate, wherein each of these three mixtures independently provide high corrosion inhibition efficiency in case of high temperature naphthenic acid corrosion inhibition and sulphur corrosion inhibition. The invention is useful in all hydrocarbon processing units, such as, refineries, distillation columns and other petrochemical industries.

FIELD OF THE INVENTION

The present invention relates to the inhibition of metal corrosion inacidic hot hydrocarbons and more particularly to the inhibition ofcorrosion of iron-containing metals in hot acidic hydrocarbons,especially when the acidity is derived from the presence of naphthenicacid. The invention is also useful for sulphur corrosion inhibition.

DISCUSSION OF PRIOR ART

It is widely known in the art that the processing of crude oil and itsvarious fractions has led to damage to piping and other associatedequipment due to naphthenic acid corrosion. These are corrosive to theequipment used to distill, extract, transport and process the crudes.Generally speaking, naphthenic acid corrosion occurs when the crudebeing processed has a neutralization number or total acid number (TAN),expressed as the milligrams of potassium hydroxide required toneutralize the acids in a one gram sample, above 0.2. It is also knownthat naphthenic acid-containing hydrocarbon is at a temperature betweenabout 200° C. and 400° C. (approximately 400° F.-750° F.), and also whenfluid velocities are high or liquid impinges on process surfaces e.g. intransfer lines, return bends and restricted flow areas.

Corrosion problems in petroleum refining operations associated withnaphthenic acid constituents and sulfur compounds in crude oils havebeen recognized for many years. Such corrosion is particularly severe inatmospheric and vacuum distillation units at temperatures between 400°F. and 790° F. Other factors that contribute to the corrosivity ofcrudes containing naphthenic acids include the amount of naphthenic acidpresent, the concentration of sulfur compounds, the velocity andturbulence of the flow stream in the units, and the location in the unit(e.g., liquid/vapor interface).

As commonly used, naphthenic acid is a collective term for certainorganic acids present in various crude oils. Although there may bepresent minor amounts of other organic acids, it is understood that themajority of the acids in naphthenic based crude are naphthenic incharacter, i.e., with a saturated ring structure as follows:

The molecular weight of naphthenic acid can extend over a large range.However, the majority of the naphthenic acid from crude oils is found ingas oil and light lubricating oil. When hydrocarbons containing suchnaphthenic acid contact iron-containing metals, especially at elevatedtemperatures, severe corrosion problems arise.

Naphthenic acid corrosion has plagued the refining industry for manyyears. This corroding material consists of predominantly monocyclic orbicyclic carboxylic acids with a boiling range between 350° and 650° F.These acids tend to concentrate in the heavier fractions during crudedistillation. Thus, locations such as the furnace tubing, transferlines, fractionating tower internals, feed and reflux sections ofcolumns, heat exchangers, tray bottoms and condensers are primary sitesof attack for naphthenic acid. Additionally, when crude stocks high innaphthenic acids are processed, severe corrosion can occur in the carbonsteel or ferritic steel furnace tubes and tower bottoms. Recentlyinterest has grown in the control of this type of corrosion inhydrocarbon processing units due to the presence of naphthenic acid incrudes from locations such as China, India, Africa and Europe.

Crude oils are hydrocarbon mixtures which have a range of molecularstructures and consequent range of physical properties. The physicalproperties of naphthenic acids which may be contained in the hydrocarbonmixtures also vary with the changes in molecular weight, as well as thesource of oil containing the acid. Therefore, characterization andbehavior of these acids are not well understood. A well known methodused to “quantify” the acid concentration in crude oil has been a KOHtitration of the oil. The oil is titrated with KOH, a strong base, to anend point which assures that all acids in the sample have beenneutralized. The unit of this titration is mg. of KOH/gram of sample andis referred to as the “Total Acid Number” (TAN) or NeutralizationNumber. Both terms are used interchangeably in the application.

The unit of TAN is commonly used since it is not possible to calculatethe acidity of the oil in terms of moles of acid, or any other of theusual analytical terms for acid content. Refiners have used TAN as ageneral guideline for predicting naphthenic acid corrosion. For example,many refineries blend their crude to a TAN=0.5 assuming that at theseconcentrations naphthenic acid corrosion will not occur. However, thismeasure has been unsuccessful in preventing corrosion by naphthenicacid.

Naphthenic acid corrosion is very temperature dependent. The generallyaccepted temperature range for this corrosion is between 205° C. and400° C. (400° F. and 750° F.). Corrosion attack by these acids below205° C. has not yet been reported in the published literature. As to theupper boundary, data suggests that corrosion rates reach a maximum atabout 600°-700° F. and then begin to diminish.

The concentration and velocity of the acid/oil mixture are alsoimportant factors which influence naphthenic acid corrosion. This isevidenced by the appearance of the surfaces affected by naphthenic acidcorrosion. The manner of corrosion can be deduced from the patterns andcolor variations in the corroded surfaces. Under some conditions, themetal surface is uniformly thinned. Thinned areas also occur whencondensed acid runs down the wall of a vessel. Alternatively, in thepresence of naphthenic acid pitting occurs, often in piping or at welds.Usually the metal outside the pit is covered with a heavy, black sulfidefilm, while the surface of the pit is bright metal or has only, a thin,grey to black film covering it. Moreover, another pattern of corrosionis erosion-corrosion, which has a characteristic pattern of gouges withsharp edges. The surface appears clean, with no visible by-products. Thepattern of metal corrosion is indicative of the fluid flow within thesystem, since increased contact with surfaces allows for a greateramount of corrosion to take place. Therefore, corrosion patterns provideinformation as to the method of corrosion which has taken place. Also,the more complex the corrosion, i.e., in increasing complexity fromuniform to pitting to erosion-corrosion, the lower is the TAN valuewhich triggers the behavior.

The information provided by corrosion patterns indicates whethernaphthenic acid is the corroding agent, or rather if the process ofcorrosion occurs as a result of attack by sulfur. Most crude containhydrogen sulfide, and therefore readily form iron sulfide films oncarbon steel. In all cases that have been observed in the laboratory orin the field, metal surfaces have been covered with a film of some sort.In the presence of hydrogen sulfide the film formed is invariably ironsulfide, while in the few cases where tests have been run in sulfur freeconditions, the metal is covered with iron oxide, as there is alwaysenough water or oxygen present to produce a thin film on the metalcoupons.

Tests utilized to determine the extent of corrosion may also serve asindicators of the type of corrosion occurring within a particularhydrocarbon treating unit. Metal coupons can be inserted into thesystem. As they are corroded, they lose material. This weight loss isrecorded in units of mg/cm.sup.2. Thereafter, the corrosion rate can bedetermined from weight loss measurements. Then the ratio of corrosionrate to corrosion product (mpy/mg/cm.sup.2) is calculated. This is afurther indicator of the type of corrosion process which has takenplace, for if this ratio is less than 10, it has been found that thereis little or no contribution of naphthenic acid to the corrosionprocess. However, if the ratio exceeds 10, then naphthenic acid is asignificant contributor to the corrosion process.

Distinguishing between sulfidation attack and corrosion caused bynaphthenic acid is important, since different remedies are requireddepending upon the corroding agent. Usually, retardation of corrosioncaused by sulfur compounds at elevated temperatures is effected byincreasing the amount of chromium in the alloy which is used in thehydrocarbon treating unit. A range of alloys may, be employed, from1.25% Cr to 12% Cr, or perhaps even higher. Unfortunately, these showlittle to no resistance to naphthenic acid. To compensate for thecorroding effects of sulfur and naphthenic acid, an austenitic stainlesssteel which contains at least 2.5% molybdenum, must be utilized. Thecorrosive problem is known to be aggravated by the elevated temperaturesnecessary to refine and crack the oil and by the oil's acidity which iscaused primarily by high levels of naphthenic acid indigenous to thecrudes. Naphthenic acids is corrosive between the range of about 175° C.to 420° C. At the higher temperatures the naphthenic acids are in thevapor phase and at the lower temperatures the corrosion rate is notserious. The corrosivity of naphthenic acids appears to be exceptionallyserious in the presence of sulfide compounds, such as hydrogen sulfide,mercaptans, elemental sulfur, sulfides, disulfides, polysulfides andthiophenols. Corrosion due to sulfur compounds becomes significant attemperatures as low as 450° F. The catalytic generation of hydrogensulfide by thermal decomposition of mercaptans has been identified as acause of sulfidic corrosion.

Sulfur in the crudes, which produces hydrogen sulfide at highertemperatures, also aggravates the problem. The temperature range ofprimary interest for this type of corrosion is in the range of about175° C. to about 400° C., especially about 205° C. to about 400° C.

Various approaches to controlling naphthenic acid corrosion haveincluded neutralization and/or removal of naphthenic acids from thecrude being processed; blending low acid number oils with corrosive highacid number oils to reduce the overall neutralization number; and theuse of relatively expensive corrosion-resistant alloys in theconstruction of the piping and associated equipment. These attempts aregenerally disadvantageous in that they require additional processingand/or add substantial costs to treatment of the crude oil.Alternatively, various amine and amide based corrosion inhibitors arecommercially available, but these are generally ineffective in the hightemperature environment of naphthenic acid corrosion. Naphthenic acidcorrosion is readily distinguished from conventional fouling problemssuch as coking and polymer deposition which can occur in ethylenecracking and other hydrocarbon processing reactions using petroleumbased feedstocks. Naphthenic acid corrosion produces a characteristicgrooving of the metal in contact with the corrosive stream. In contrast,coke deposits generally have corrosive effects due to carburization,erosion and metal dusting.

Because these approaches have not been entirely satisfactory, theaccepted approach in the industry is to construct the distillation unit,or the portions exposed to naphthenic acid/sulfur corrosion, with theresistant metals such as high quality stainless steel or alloyscontaining higher amounts of chromium and molybdenum. The installationof corrosion-resistant alloys is capital intensive, as alloys such as304 and 316 stainless steels are several times the cost of carbon steel.However, in units not so constructed there is a need to provideinhibition treatment against this type of corrosion. The prior artcorrosion inhibitors for naphthenic acid environments includenitrogen-based filming corrosion inhibitors. However, these corrosioninhibitors are relatively ineffective in the high temperatureenvironment of naphthenic acid oils.

While various corrosion inhibitors are known in various arts, theefficacy and usefulness of any particular corrosion inhibitor isdependent on the particular circumstances in which it is applied. Thus,efficacy or usefulness under one set of circumstances often does notimply the same for another set of circumstances. As a result, a largenumber of corrosion inhibitors have been developed and are in use forapplication to various systems depending on the medium treated, the typeof surface that is susceptible to the corrosion, the type of corrosionencountered, and the conditions to which the medium is exposed. Forexample, U.S. Pat. No. 3,909,447 describes certain corrosion inhibitorsas useful against corrosion in relatively low temperature oxygenatedaqueous systems such as water floods, cooling towers, drilling muds, airdrilling and auto radiator systems. That patent also notes that manycorrosion inhibitors capable of performing in non-aqueous systems and/ornon-oxygenated systems perform poorly in aqueous and/or oxygenatedsystems. The reverse is true as well. The mere fact that an inhibitorthat has shown efficacy in oxygenated aqueous systems does not suggestthat it would show efficacy in a hydrocarbon. Moreover, the mere factthat an inhibitor has been efficacious at relatively low temperaturesdoes not indicate that it would be efficacious at elevated temperatures.In fact, it is common for inhibitors that are very effective atrelatively low temperatures to become ineffective at temperatures suchas the 175° C. to 400° C. encountered in oil refining. At suchtemperatures, corrosion is notoriously troublesome and difficult toalleviate. Thus, U.S. Pat. No. 3,909,447 contains no teaching orsuggestion that it would be effective in non-aqueous systems such ashydrocarbon fluids, especially hot hydrocarbon fluids. Nor is there anyindication in U.S. Pat. No. 3,909,447 that the compounds disclosedtherein would be effective against naphthenic acid corrosion under suchconditions.

Atmospheric and vacuum distillation systems are subject to naphthenicacid corrosion when processing certain crude oils. Currently usedtreatments are thermally reactive at use temperatures. In the case ofphosphorus-based inhibitors, this is thought to lead to a metalphosphate surface film. The film is more resistant to naphthenic acidcorrosion than the base steel. These inhibitors are relatively volatileand exhibit fairly narrow distillation ranges. They are fed into acolumn above or below the point of corrosion depending on thetemperature range. Polysulfide inhibitors decompose into complexmixtures of higher and lower polysulfides and, perhaps, elemental sulfurand mercaptans. Thus, the volatility and protection offered is notpredictable.

The problems caused by naphthenic acid corrosion in refineries and theprior art solutions to that problem have been described at length in theliterature, the following of which are representative:

U.S. Pat. No. 3,531,394 to Koszman described the use of phosphorusand/or bismuth compounds in the cracking zone of petroleum steamfurnaces to inhibit coke formation on the furnace tube walls.

U.S. Pat. No. 3,531,394 to Koszman described the use of phosphorusand/or bismuth compounds in the cracking zone of petroleum steamfurnaces to inhibit coke formation on the furnace tube walls.

U.S. Pat. No. 4,024,049 to Shell et al discloses compounds substantiallyas described and claimed herein for use as refinery antifoulants. Whileeffective as antifoulant materials, materials of this type have notheretofore been used as corrosion inhibitors in the manner set forthherein. While this reference teaches the addition of thiophosphateesters such as those used in the subject invention to the incoming feed,due to the non-volatile nature of the ester materials they do notdistill into the column to protect the column, the pump around piping,or further process steps. I have found that by injecting thethiophosphate esters as taught herein, surprising activity is obtainedin preventing the occurrence of naphthenic acid corrosion indistillation columns, pump around piping, and associated equipment.

U.S. Pat. No. 4,105,540 to Weinland describes phosphorus containingcompounds as antifoulant additives in ethylene cracking furnaces. Thephosphorus compounds employed are mono- and di-ester phosphate andphosphite compounds having at least one hydrogen moiety complexed withan amine.

U.S. Pat. No. 4,443,609 discloses certain tetrahydrothiazole phosphonicacids and esters as being useful as acid corrosion inhibitors. Suchinhibitors can be prepared by reacting certain 2,5-dihydrothiazoles witha dialkyl phosphite. While these tetrahydrothiazole phosphonic acids oresters have good corrosion and inhibition properties, they tend to breakdown during high temperature applications thereof with possible emissionof obnoxious and toxic substances.

It is also known that phosphorus-containing compounds impair thefunction of various catalysts used to treat crude oil, e.g., infixed-bed hydrotreaters and hydrocracking units. Crude oil processorsare often in a quandary since if the phosphite stabilizer is not used,then iron can accumulate in the hydrocarbon up to 10 to 20 ppm andimpair the catalyst. Although nonphosphorus-containing inhibitors arecommercially available, they are generally less effective than thephosphorus-containing compounds.

U.S. Pat. No. 4,542,253 to Kaplan et al, described an improved method ofreducing fouling and corrosion in ethylene cracking furnaces usingpetroleum feedstocks including at least 10 ppm of a water soluble minecomplexed phosphate, phosphite, thiophosphate or thiophosphite estercompound, wherein the amine has a partition coefficient greater than 1.0(equal solubility in both aqueous and hydrocarbon solvents).

U.S. Pat. No. 4,842,716 to Kaplan et al describes an improved method forreducing fouling and corrosion at least 10 ppm of a combination of aphosphorus antifoulant compound and a filming inhibitor. The phosphoruscompound is a phosphate, phosphite, thiophosphate or thiophosphite estercompound. The filming inhibitor is an imidazoline compound.

U.S. Pat. No. 4,941,994 Zetmeisl et al discloses a naphthenic acidcorrosion inhibitor comprising a dialkyl or trialkylphosphite incombination with an optional thiazoline.

A significant advancement in phosphorus-containing naphthenic acidcorrosion inhibitors was reported in U.S. Pat. No. 4,941,994. Therein itis disclosed that metal corrosion in hot acidic liquid hydrocarbons isinhibited by the presence of a corrosion inhibiting amount of a dialkyland/or trialkyl phosphite with an optional thiazoline.

While the method described in U.S. Pat. No. 4,941,994 providessignificant improvements over the prior art techniques, nevertheless,there is always a desire to enhance the ability of corrosion inhibitorswhile reducing the amount of phosphorus-containing compounds which mayimpair the function of various catalysts used to treat crude oil, aswell as a desire for such inhibitors that may be produced from lowercost or more available starting materials.

Another approach to the prevention of naphthenic acid corrosion is theuse of a chemical agent to form a barrier between the crude and theequipment of the hydrocarbon processing unit. This barrier or filmprevents corrosive agents from reaching the metal surface, and isgenerally a hydrophobic material.

Gustaysen et al. NACE Corrosion 89 meeting, paper no. 449, Apr. 17-21,1989 details the requirements for a good filming agent. U.S. Pat. No.5,252,254 discloses one such film forming agent, sulfonatedalkyl-substituted phenol, and effective against naphthenic acidcorrosion.

U.S. Pat. No. 5,182,013 issued to Petersen et al. on Jan. 26, 1993describes another method of inhibiting naphthenic acid corrosion ofcrude oil, comprising introducing into the oil an effective amount of anorganic polysulfide. The disclosure of U.S. Pat. No. 5,182,013 isincorporated herein by reference. This is another example of acorrosion-inhibiting sulfur species. Sulfidation as a source ofcorrosion was detailed above. Though the process is not well understood,it has been determined that while sulfur can be an effectiveanti-corrosive agent in small quantities, at sufficiently highconcentrations, it becomes a corrosion agent.

Phosphorus can form an effective barrier against corrosion withoutsulfur, but the addition of sulfiding agents to the process streamcontaining phosphorus yields a film composed of both sulfides andphosphates. This results in improved performance as well as a decreasedphosphorus requirement. This invention pertains to the deliberateaddition of sulfiding agents to the process stream when phosphorus-basedmaterials are used for corrosion control to accentuate this interaction.

U.S. Pat. No. 5,314,643 to Edmondson et al., describes a process forinhibition of corrosion caused by naphthenic acid and sulphur compoundsduring the elevated temperature processing of crude oil by use of acorrosion inhibitor consisting of a combination of trialkylphosphate andan alkaline earth metal phosphonate-phenate sulphide, functioningeffectively as an inhibitor on the internal metallic surfaces of theequipment used in crude oil refining operations.

Organic polysulfides (Babaian-Kibala, U.S. Pat. No. 5,552,085), organicphosphites (Zetlmeisl, U.S. Pat. No. 4,941,994), and phosphate/phosphiteesters (Babaian-Kibala, U.S. Pat. No. 5,630,964), have been claimed tobe effective in hydrocarbon-rich phase against naphthenic acidcorrosion. However, their high oil solubility incurs the risk ofdistillate side stream contamination by phosphorus.

Phosphoric acid has been used primarily in aqueous phase for theformation of a phosphate/iron complex film on steel surfaces forcorrosion inhibition or other applications (Coslett, British patent8,667, U.S. Pat. Nos. 3,132,975, 3,460,989 and 1,872,091). Phosphoricacid use in high temperature non-aqueous environments (petroleum) hasalso been reported for purposes of fouling mitigation (U.S. Pat. No.3,145,886).

There remains a continuing need to develop additional options formitigating the corrosivity of acidic crudes at lower cost. This isespecially true at times of low refining margins and a high availabilityof corrosive crudes from sources such as Europe, China, or Africa, andIndia. The present invention addresses this need.

OBJECTS AND ADVANTAGES OF PRESENT INVENTION

Accordingly, the objects and advantages of the present invention aredescribed below.

An object of present invention is to provide a chemical compositionwhich will provide very effective high temperature naphthenic acidcorrosion inhibition as well as sulphur corrosion inhibition.

Another object of the present invention is to provide a corrosioninhibiting composition, which is very stable even at high temperature.

Yet another object of the present invention is to provide a corrosioninhibiting composition, having very low acid value.

SUMMARY OF INVENTION

The present invention relates to the field of processing hydrocarbonswhich causes corrosion in the metal surfaces of processing units. Theinvention addresses the technical problem of high temperature naphthenicacid corrosion and sulphur corrosion and provides a solution to inhibitthese types of corrosion. The three combination compositions are formedby three mixtures separately, with one mixture obtained by mixingcompound A, which is obtained by reacting high reactive polyisobutylene(HRPIB) with phosphorous pentasulphide in presence of catalytic amountof sulphur with compound B such as trialkyl phosphate and second mixtureobtained by mixing compound A with compound C such as phosphite likedi-isodecyl phenyl phosphite, and third mixture obtained by mixingcompound A with compound D such as a phosphonate, wherein each of thesethree mixtures independently provide high corrosion inhibitionefficiency in case of high temperature naphthenic acid corrosioninhibition and sulphur corrosion inhibition. The invention is useful inall hydrocarbon processing units, such as, refineries, distillationcolumns and other petrochemical industries.

DESCRIPTION OF THE INVENTION

It has been surprisingly discovered by the inventor of the presentinvention, that a combination of organophosphorus sulphur compound andany of other phosphorus compounds such as, phosphates, phosphites andphosphonates, is very efficiently functioning in controlling naphthenicacid corrosion, providing a synergetic effect of combination ofPhosphorus compounds. The organophosphorus sulphur compound is made fromreaction of hydrocarbon R₁ such as olefins with, phosphoruspentasulphide, in presence of sulphur powder. Amongst the otherPhosphorus compounds tributylphosphate and di-isodecyl phenyl phosphiteare the preferred ones.

The preferred olefins have double bonds, wherein double bond is presentinternally or terminally. The details about such hydrocarbon R₁ aregiven below:

As previously mentioned, the term “hydrocarbon” as used herein means anyone of an alkyl group, an alkenyl group, an alkynyl group, which groupsmay be linear, branched or cyclic, or an aryl group. The termhydrocarbon also includes those groups but wherein they have beenoptionally substituted. If the hydrocarbon is a branched structurehaving substituent(s) thereon, then the substitution may be on eitherthe hydrocarbon backbone or on the branch; alternatively thesubstitutions may be on the hydrocarbon backbone and on the branch.

Preferably R₁ is an optionally substituted alkyl or alkenyl group. Inone aspect R₁ is an optionally substituted alkyl group. In anotheraspect, R₁ is an optionally substituted alkenyl group.

The term “alkenyl” refers to a branched or straight chain hydrocarbon,which can comprise one or more carbon-carbon double bonds. Exemplaryalkenyl groups include propylenyl, butenyl, isobutenyl, pentenyl,2,2-methylbutenyl, 3-methylbutenyl, hexanyl, heptenyl, octenyl, andpolymers thereof.

In one aspect R₁ is an optionally substituted branched alkyl or alkenylgroup. Preferably, R₁ is a polyisobutenyl (PIB) group.

Conventional PIBs and so-called “high-reactivity” PIBs (see for exampleEP-B-0565285) are suitable for use in this invention. High reactivity inthis context is defined as a PIB wherein at least 50%, preferably 70% ormore, of the terminal olefinic double bonds are of the vinylidene type,for example the GLISSOPAL compounds available from BASF.

In one aspect R₁ has between 10 and 1000 carbon atoms, preferablybetween 4 and 200 carbon atoms.

In one aspect, R₁ has a molecular weight of from 200 to 10000,preferably from 200 to 1300.

The trialkylphosphate such as tributyl phosphate will contain an alkylmoiety of C₁-C₁₂ such that those compounds contemplated as having thedesired efficacy and within the disclosure of the present inventioninclude trimethylphosphate, triethylphosphate, tripropylphosphate,tributylphosphate and tripentylphosphate. Due to its easy commercialavailability, tributylphosphate may be considered the preferredcompound.

The most effective amount of the corrosion inhibitor to be used inaccordance with the present invention can vary depending on the localoperating conditions and the particular hydrocarbon being processed.Thus, the temperature and other characteristics of the acid corrosionsystem can have a bearing on the amount of inhibitor or mixture ofinhibitors to be used. Generally, where the operating temperaturesand/or the acid concentrations are higher, a proportionately higheramount of the corrosion inhibitor will be required. It has been foundthat the concentration of the corrosion inhibitors or mixture ofinhibitors added to the crude oil may range from about 1 ppm to 5000ppm. It has also been found that it is preferred to add the inhibitorsat a relatively high initial dosage rate of 2000-3000 ppm and tomaintain this level for a relatively short period of time until thepresence of the inhibitor induces the build-up of a corrosion protectivecoating on the metal surfaces.

Once the protective surface is established, the dosage rate needed tomaintain the protection may be reduced to a normal operational range ofabout 100-1500 ppm without substantial sacrifice of protection.

The inventor of the present invention has carried out extensiveexperimentation to verify the effectiveness of corrosion-inhibition incase naphthenic acid corrosion, by experimenting with differentproportions of compound A, that is, polyisobutylene plus phosphoruspentasulphide plus sulphur powder and compound B, that is, tributylphosphate in the abovementioned combination of these compounds.Experiments were also preformed by using compound A alone and compound Balone separately.

The inventor of the present invention has also carried out extensiveexperimentation to verify the effectiveness of corrosion-inhibition incase naphthenic acid corrosion, by experimenting with differentproportions of compound A, that is, polyisobutylene plus phosphoruspentasulphide plus sulphur powder and compound C, that is, di-isodecylphenyl phosphite in the abovementioned combination of these compounds.Experiments were also preformed by using compound A alone and compound Balone and compound C alone, separately.

The reacted compound “A” is obtained by reaction of olefins with P₂S₅(Phosphorus pentasulphide) in presence of sulphur powder. The preferredolefins have double bonds, wherein double bond is present internally orterminally.

The example of internally double bonded olefins include beta-olefins.

The example of terminally double bonded olefins include alpha-olefins.These olefins have 5 to 30 carbon atoms. These olefins arealternatively, polymeric olefins such as high reactive polyisobutylenecontaining greater than 70% of vinyledene double bond, and normalpolysobutylenes which contains Vinyl, vinyledene, and such other groupsof chemicals.

The ratio of P₂S₅ to Olefin is preferably 0.05 to 2 mole of P₂S₅ to 1mole of Olefins. The Sulphur powder is present in catalytic quantity,that is, sulphur powder is 0.5% to 5% of Olefin by weight.

The most preferred embodiment of the present invention is describedbelow: A weighed quantity of HRPIB (High Reactive Polyisobutylene),Phosphorus pentasulphide and sulphur powder are charged into a cleanfour-necked round bottom flask, equipped with nitrogen inlet, stirrerand thermometer, thereby forming a reaction mixture.

This reaction mixture is stirred and heated to temperature of 160° C.under nitrogen gas purging. At this temperature of 160° C., the reactionleads to evolution of hydrogen sulphide gas (H₂S). The temperature ofthe reaction mixture is now maintained between 160° C. to 180° C., for aperiod of 1 hour to 2 hours. Then the temperature of the mixture israised to 220° C. The reaction mixture is then maintained at thistemperature of 220° C. for 6 hours.

The resultant reaction mass is then cooled to temperature of 100° C.,when nitrogen gas is purged into the resultant reaction mass, to driveout the hydrogen sulphide present therein. The resulting polyisobutylenePhosphorus sulphur compound is used as a high temperature naphthenicacid corrosion inhibitor. This compound is used neat or diluted inappropriate solvent such as xylene, toluene, and aromatic solvent as anyother appropriate solvent to achieve inhibition of high temperaturenaphthenic acid corrosion.

The present invention is directed to a method for inhibiting corrosionon the metal surfaces of the processing units which process hydrocarbonssuch as crude oil and its fractions containing naphthenic acid. Theinvention is explained in details in its simplest form wherein thefollowing method steps are carried out, when it is used to process crudeoil in process units such as distillation unit. Similar steps can beused in different processing units such as, pump around piping, heatexchangers and such other processing units.

These method steps are explained below:

-   -   a) heating the hydrocarbon containing naphthenic acid to        vaporize a portion of the hydrocarbon:    -   b) allowing the hydrocarbon vapors to rise in a distillation        column;    -   c) condensing a portion of the hydrocarbon vapours passing        through the distillation column to produce a distillate;    -   d) adding to the distillate, from 1 to 5000 ppm of a combination        compound (A+B) or combination compound (A+C) of instant        invention;    -   e) allowing the distillate containing combination compound (A+B)        or combination compound (A+C) to contact substantially the        entire metal surfaces of the distillation unit to form        protective film on such surface, whereby such surface is        inhibited against corrosion.

It is advantageous to treat distillation column, trays, pump aroundpiping and related equipment to prevent naphthenic acid corrosion, whencondensed vapours from distilled hydrocarbon fluids contact metallicequipment at temperatures greater than 200° C., and preferably 400° C.The combination compound (A+B) or combination compound (A+C) as additiveis generally added to the condensed distillate and the condenseddistillate is allowed to contact the metallic surfaces of thedistillation column, packing, trays, pump around piping and relatedequipment as the condensed distillate passes down the column and intothe distillation vessel. The distillate may also be collected asproduct. The corrosion inhibitors of the instant invention remain in theresultant collected product.

In commercial practice, the additives of this invention may be added toa distillate return to control corrosion in a draw tray and in thecolumn packing while a second injection may be added to a spray oilreturn immediately below the draw trays to protect the tower packing andtrays below the distillate draw tray. It is not so critical where theadditive of the invention is added as long as it is added to distillatethat is later returned to the distillation vessel, or which contact themetal interior surfaces of the distillation column, trays, pump aroundpiping and related equipments.

The method of using the polyisobutylene phosphorus sulphur compound ofthe present invention for achieving inhibition of high temperaturenaphthenic acid corrosion is explained below with the help of examples 1and 2.

Example 3 shows use of compound B.

Example 4 shows use of combination compound (A+B).

Example 5 shows use of compound C.

Example 6 shows use of combination compound (A+C).

The compound B of the combination compound (A+B) of the presentinvention is easily obtained commercially.

The compound C of the combination compound (A+C) of the presentinvention is easily obtained commercially.

Example 1

The weighed quantities of 68.16 gm of commercially available HRPIB (HighReactive Polyisobutylene with molecular weight 950 approximately), 30.31gm of Phosphorus Pentasulphide and 1.51 gm of Sulphur Powder are chargedinto a clean four necked round bottom flask, equipped with N₂ inlet,stirrer and thermometer, thereby forming a reaction mixture. This gives1:1 mole ratio of Phosphorus Pentasulphide to Olefin.

The reaction mixture was stirred and heated to 160° C. temperature undernitrogen gas purging. The purging of N₂ gas led to removal of hydrogensulphide gas, which was generated during the reaction. The temperatureof the reaction mixture was maintained between 160° C. to 180° C., for aperiod of 1 hour to 2 hours. Then the temperature of the mixture wasraised to 220° C. and the mixture was maintained at this temperature for6 to 10 hours.

The resultant reaction mass was then cooled to 100° C. when nitrogen gaswas purged into it, to drive out the hydrogen sulphide gas presenttherein. The resulting polyisobutylene Phosphorus sulphur compound wasused as a high temperature naphthenic acid corrosion inhibitor, as wellas, sulphur corrosion inhibitor. This compound was used neat or dilutedin appropriate solvent such as xylene, toluene, and aromatic solvent aswell as any other appropriate solvent to achieve inhibition of hightemperature naphthenic acid corrosion as well as sulphur corrosion.

The above mentioned synthesis is carried out for different molar ratiosof 1:1, 1:0.5 and 1:0.25 of HRPIB to Phosphorus Pentasulphide. A similarsynthesis was carried out by using normal polyisobutylene instead ofHRPIB, with molar ratio of 1:0.35.

Example 2 High Temperature Naphthenic Acid Corrosion Test

In this example, various amounts of a 50% formulation of the compositionprepared in accordance, with Example 1, were tested for corrosioninhibition efficiency on steel coupons in hot oil containing naphthenicacid. A weight loss coupon, immersion test was used to evaluate theinvention compound for its effectiveness in inhibition of naphthenicacid corrosion at 290° C. temperature. Different dosage such as 300, 400and 600 ppm of invention compound were used, as 50% active solution.

A corrosion inhibition test on steel coupon was conducted without usingany additive. This test provided a blank test reading.

The reaction apparatus consisted of a one-litre four necked round bottomflask equipped with water condenser, N₂ purger tube, thermometer pocketwith thermometer and stirrer rod. 600 gm (about 750 ml) paraffinhydrocarbon oil (D-130) was taken in the flask. N₂ gas purging wasstarted with flow rate of 100 cc/minute and the temperature was raisedto 100° C., which temperature was maintained for 30 minutes. A compoundof example 1 comprising Polyisobutylene and Phosphorus Pentasulphidewith sulphur powder was added to the reaction mixture. The reactionmixture was stirred for 15 minutes at 100° C. temperature. Afterremoving the stirrer, the temperature of the reaction mixture was raisedto 290° C. A pre-weighed weight-loss carbon steel coupon CS 1010 withdimensions 76 mm×13 mm×1.6 mm was immersed. After maintaining thiscondition for 1 hour to 1.5 hours, 31 gm of naphthenic acid (commercialgrade with acid value of 230 mg/KOH) was added to the reaction mixture.A sample of one gm weight of reaction mixture was collected fordetermination of acid value, which was found to be approximately 11.7.This condition was maintained for four hours. After this procedure, themetal coupon was removed, excess oil was rinsed away, and the excesscorrosion product was removed from the metal surface. Then the metalcoupon was weighed and the corrosion rate was calculated in mils peryear.

Calculation of Corrosion Inhibition Efficiency.

The method used in calculating Corrosion Inhibition Efficiency is givenbelow. In this calculation, corrosion inhibition efficiency provided byadditive compound is calculated by comparing weight loss due to additivewith weight loss of blank coupon (without any additive).

${{Corrosion}\mspace{14mu} {Inhibition}\mspace{14mu} {Efficiency}} = {\frac{\begin{matrix}{\left( {{Weight}\mspace{14mu} {loss}\mspace{14mu} {for}\mspace{14mu} {blank}\mspace{14mu} {without}\mspace{14mu} {additive}} \right) -} \\\left( {{weight}\mspace{14mu} {loss}\mspace{14mu} {with}\mspace{14mu} {additive}} \right)\end{matrix}}{\left( {{weight}\mspace{14mu} {loss}\mspace{14mu} {for}\mspace{14mu} {blank}\mspace{14mu} {without}\mspace{14mu} {additive}} \right)} \times 100}$

The calculated magnitudes are entered in the Tables in appropriatecolumns.

The results of the experiments are presented in Table I and II.

The test results of the experiments conducted by using normalpolyisobutylene are given in Table III.

The corrosion rate in MPY (mils per year) is calculated by the formula,

${M\; P\; Y} = \frac{534 \times {Weight}\mspace{14mu} {loss}\mspace{14mu} {in}\mspace{14mu} {mg}}{\left( {{Density}\mspace{14mu} {in}\mspace{14mu} {gm}\text{/}{cc}} \right) \times \left( {{Area}\mspace{14mu} {in}\mspace{14mu} {in}^{2}} \right) \times \left( {{Time}\mspace{14mu} {of}\mspace{14mu} {test}\mspace{14mu} {in}\mspace{14mu} {hours}} \right)}$

Example 3

Experiments were carried out by the inventor of the present invention,to test the effectiveness of a commercially available phosphoruscompound B, such as tributyl phosphate, in inhibition of naphthenic acidcorrosion. Different dosages of tributyl phosphate, such as 75, 90 and100 ppm were used in the experiments. The result of some of theseexperiments are presented in Table 5.

Example 4

Experiments were carried out by the inventor of the present invention,to test the synergetic effectiveness of a combination of the compounds Aand B, where compound A represents high reactive polyisobutylene plusPhosphorus pentasulphide plus sulphur powder and compound B representstributyl phosphate (compound B is used as available commercially).Different total dosages of inhibitor combination compound's combinationsuch as 300 ppm and 400 ppm were used in the experimentation. Similarly,different proportions of compound A and compound B, were used in theseexperiments. These different percentage proportions of A:B were 67:33,70:30, 75:25, and 81:19. The result of these experiments are presentedin Tables 6 to 8.

Example 5

By using the method steps similar to that of example 2, the experimentswere carried out by the inventor of the present invention, to test theeffectiveness of another commercially available Phosphorus compound C,such as Di-isodecyl Phenyl Phosphite, in inhibition of naphthenic acidcorrosion. Different active dosages of Di-isodecyl Phenyl Phosphite,such as 75, 90, 120 and 150 ppm were used in the experiments. Theresults of these experiments are presented in Table 9.

Example 6

By using the method steps similar to that of example 5, the experimentswere carried out by the inventor of the present invention, to testsynergetic effectiveness of a combination of the compounds A and C, ininhibition of naphthenic acid corrosion, where compound A representshigh reactive polyisobutylene plus phosphorus pentasulphide pluscatalytic amount of sulphur powder and compound C represents Di-isodecylPhenyl Phosphite, (Compound C is used as available commercially).Different total active dosages of inhibitor combination compound'scombination such as 195, 200, 210, 250, 300 ppm were used in theexperimentation. Similarly these total active dosages included differentproportions of active compounds A and C. These different proportions ofA:C included 105:90, 90:120, 100:100, 140:60, 110:90, 130:120 and180:120 the results of these experiments are presented in Table 10.

TABLE 1 CORROSION INHIBITION TEST (with molar ratio of Polyisobutyleneto Phosphorus Pentasulphide = 1:1) (EXAMPLE - 2) Corrosion EffectiveWeight Inhibition Inhibitor Dosage in Dosage in Loss in Corrosionefficiency Expt. No. Compound ppm ppm mg Rate in MPY in % 1 (Only blank)— — 89.5 529.89 0 2 Composition as 200 100 63.3 371.23 29.27 per Example1 3 Composition as 300 150 39.6 232.24 55.75 per Example 1 4 Compositionas 400 200 15.2 89.114 83.02 per Example 1 5 Composition as 600 300 3.812.31 95.75 per Example 1 6 Composition as 650 325 0.3 1.5 99.67 perExample 1

TABLE 2 CORROSION INHIBITION TEST (with molar ratio of Polyisobutyleneto Phosphorus Pentasulphide = 1:0.5) (EXAMPLE - 2) Corrosion DosageEffective Weight Corrosion Inhibition Inhibitor in Dosage Loss in Ratein Efficiency Experiment No. Compound ppm in ppm mg MPY in % 15 — — —87.7 439 0 (Only blank) 7 Composition 500 250 21.5 107.62 75.48 as perExample 1

TABLE 3 CORROSION INHIBITION TEST (with molar ratio of Polyisobutyleneto Phosphorus Pentasulphide = 1:0.25) (EXAMPLE - 2) Corrosion DosageEffective Weight Corrosion Inhibition Inhibitor in Dosage Loss in Ratein efficiency Experiment No. Compound ppm in ppm mg MPY in % 15 — — —87.7 439 0 (Only blank) 8 Composition 500 250 50.6 253.3 42.3 as perExample 1 9 Composition 1000 500 14.2 71.08 83.81 as per Example 1 10Composition 1500 750 2.0 10.1 97.72 as per Example 1

TABLE 4 CORROSION INHIBITION TEST (with molar ratio of NormalPolyisobutylene to Phosphorus Pentasulphide = 1:0.35) Corro- CorrosionDosage Effective Weight sion Inhibition Expt. Inhibitor in Dosage Lossin Rate in efficiency No. Compound ppm in ppm mg MPY in % 15 — — — 87.7439 0 (Only blank) 11 Composition 600 300 40 200.21 54.39 as per Example1

TABLE 5 CORROSION INHIBITION TEST (Inhibitor compound B = TributylPhosphate) Corrosion Weight Inhibition Experiment Inhibitor Dosage Lossin Corrosion efficiency No. Compound in ppm mg Rate MPY in % 1 — — 89.5529.89 0 (Only blank) 12 Tributyl 75 55.5 325.49 37.99 Phosphate (ascommercially available) without any solvent 13 Compound as 90 21.95128.73 75.48 per Experiment No 12 14 Compound as 100 14.35 84.16 83.97per Experiment No 12

TABLE 6 CORROSION INHIBITION TEST (Inhibitor compound = A + B) Dosage in(ppm) Corrosion Total Weight Corrosion Inhibition Expt. Inhibitor Dosageloss Rate in efficiency No. M.R compound Compound A Compound B A + B(mg) (MPY) (%) 15 — (Blank) — — — 87.70 439 0 16 1:1 A + B 120 80 200 010 100 17 1:1 A + B 150 75 225 2.2 11.01 97.49 18 1:1 A + B 180 60 2400.7 3.5 99.20 Compound A = 50% of Polyisobutylene plus PhosphorusPentasulphide + Catalytic amount of Sulphur Powder (as per example 1)and 50% solvent Compound B = Tributyl Phosphate (as commerciallyavailable) without any solvent. M.R. = Molar Ratio of Polyisobutylene toPhosphorus Pentasulphide

TABLE 7 CORROSION INHIBITION TEST (Inhibitor compound = A + B) Dosage in(ppm) Corrosion Total Weight Corrosion Inhibition Expt. Inhibitor Dosageloss Rate in efficiency No. M.R. compound Compound A Compound B A + B(mg) (MPY) (%) 1 — (Only blank) — — — 89.5 529.89 0 19 1:1 A + B 200 100300 2.73 16.01 96.95 20 1:1 A + B 210 90 300 2.90 17.00 96.76 21 1:1 A +B 225 75 300 5.30 31.08 94.08 22 1:1 A + B 325 75 400 4.70 27.56 94.75Compound A = 50% of Polyisobutylene plus Phosphorus Pentasulphide +Catalytic amount of Sulphur Powder (as per example 1) and 50% solventCompound B = Tributyl Phosphate (as commercially available) without anysolvent. M.R. = Molar Ratio of Polyisobutylene to PhosphorusPentasulphide

TABLE 8 CORROSION INHIBITION TEST (Inhibitor compound = A + B) CorrosionDosage in (ppm) Weight Corrosion. Inhibition Experiment Inhibitor TotalDosage loss Rate in efficiency No. M.R. comp. Comp. A Comp. B A + B (mg)(MPY) (%) 15 — (Only — — — 87.7 439 0 blank) 23 1:0.5 A + B 300 75 3751.8 9.01 97.95 24 1:0.5 A + B 330 60 390 5.2 26.03 94.07 25 1:0.5 A + B255 45 300 39.4 197.21 55.07 Compound A = 50% of Polyisobutylene plusPhosphorus Pentasulphide + Catalytic amount of Sulphur Powder (as perexample 1) and 50% solvent Compound B = Tributyl Phosphate (ascommercially available) without any solvent. M.R. = Molar Ratio ofPolyisobutylene to Phosphorus Pentasulphide

TABLE 9 CORROSION INHIBITION TEST (Inhibitor compound C = Di-isodecylPhenyl Phosphite as commercially available without any solvent)Corrosion Exper- Dosage Weight Corrosion Inhibition iment Inhibitor inLoss in Rate in efficiency No. Compound ppm mg MPY in % 15 (Only blank)— 87.70 439 0 26 Di-isodecyl Phenyl 75 73.90 369.90 15.74 Phosphitewithout any solvent 27 Compound as per 90 58.5 292.81 33.30 ExperimentNo 26 28 Compound as per 120 21.0 105.11 76.05 Experiment No 26 29Compound as per 150 1.60 8.01 98.18 Experiment No 26

TABLE 10 CORROSION INHIBITION TEST (Inhibitor compound = A + C)Corrosion Dosage in (ppm) Weight Corrosion Inhibition Expt. InhibitorTotal Dosage loss Rate in efficiency No. M.R. compound Comp. A Comp. CA + C (mg) (MPY) (%) 15 — (Only — — — 87.7 439 0 blank) 30 1:1 A + C 21090 300 4.9 24.53 94.41 31 1:1 A + C 180 120 300 0.7 3.5 99.20 32 1:1 A +C 200 100 300 0.3 1.5 99.66 33 1:1 A + C 280 60 340 0.4 2.0 99.54 34 1:1A + C 220 90 310 0.1 0.5 99.89 35   1:0.5 A + C 260 120 380 1.5 7.5198.29 36   1:0.5 A + C 360 120 480 3.4 17.02 96.12 Compound A = 50% ofPolyisobutylene plus Phosphorus Pentasulphide + Catalytic amount ofSulphur Powder (as per example 1) and 50% solvent Compound C =Di-isodecyl Phenyl Phosphite as commercially available without anysolvent

TABLE 11 CORROSION INHIBITION TEST (Inhibitor compound = A + B)Corrosion Dosage in (ppm) Weight Corrosion. Inhibition Expt. InhibitorTotal Dosage loss Rate in efficiency No. M.R. comp. Comp. A Comp. B A +B (mg) (MPY) (%) 15 — (Only — — — 87.7 439 0 blank) 37 1:0.35 A + B 32090 410 1.3 6.5 98.52 Compound A = 50% of Normal Polyisobutylene plusPhosphorus Pentasulphide + Catalytic amount of Sulphur Powder (as perexample 1) and 50% solvent Compound B = Tributyl Phosphate (ascommercially available) without any solvent. M.R. = Molar Ratio ofPolyisobutylene to Phosphorus Pentasulphide

TABLE 12 CORROSION INHIBITION TEST (Inhibitor compound = A + C)Corrosion Dosage in (ppm) Weight Corrosion Inhibition Expt. InhibitorTotal Dosage loss Rate in efficiency No. M.R. compound Comp. A Comp. CA + C (mg) (MPY) (%) 15 — (Only blank) — — — 87.7 439 0 38 1:0.35 A + C360 120 480 24.2 121 72.41 Compound A = 50% of Normal Polyisobutyleneplus Phosphorus Pentasulphide + Catalytic amount of Sulphur Powder (asper example 1) and 50% solvent Compound C = Di-isodecyl Phenyl Phosphiteas commercially available without any solvent

Discussion of the Results Presented in Tables

The detailed discussion given below with respect to the resultspresented in Tables 1 to 12 for the experiments described an Examples 1to 6 explains the effectiveness of the additive inhibitor compounds ofpresent invention in high temperature naphthenic acid corrosioninhibition or sulphur corrosion inhibition.

The additive inhibitor compound of the present invention, which is veryeffective in inhibition of high temperature naphthenic acid corrosion,comprises a mixture of a compound A with either of the two compounds Band C, wherein,

A=50% of reaction product of Polyisobutylene plus PhosphorusPentasulphide+Catalytic amount of Sulphur Powder (as per example 1) and50% solvent.

B=Tributyl Phosphate, (as commercially available), without any solvent.

C=Di-isodecyl Phenyl Phosphite, (as commercially available), without anysolvent.

The results presented in the Tables 1 to 12, show separately theeffectiveness of each of the three compounds A, B, and C and also showseparately the effectiveness of the each of the two mixture (A+B) and(A+C). The detailed discussion given below, shows very much improvedeffectiveness in high temperature naphthenic acid corrosion inhibition,of each of the two mixtures (A+B) and (A+C), as compared toeffectiveness of each of the compounds. A, B and C separately. The verymuch improved effectiveness of the inhibiting compound of presentinvention, that is of either of mixtures (A+B) or (A+C) is seen from thevery high corrosion inhibition efficiency, even with reduction in thetotal dosage of the active components.

Tables 1 to 3 show the results of effectiveness of compound A, for threedifferent molar ratio of high Reactive Polyisobutylene to PhosphorusPentasulphide, such as 1:1, 1:0.5 and 1:0.25. Table 4 shows results ofeffectiveness of compound A with molar ratio of Normal Polyisobutyleneto Phosphorus Pentasulphide, such as 1:0.35.

Table 5 shows results of effectiveness of compound B that is, TributylPhosphate, as commercially available, without any solvent.

Table 9 shows results of effectiveness of compound C, that isDi-isodecyl Phenyl Phosphite, as commercially available, without anysolvent.

Three tables 6 to 8 show effectiveness of the additive compoundcomprising mixture (A+B) of present invention, with two molar ratios 1:1and 1:0.5 of two components of A, that is, High Reactive Polyisobutyleneand Phosphorus Pentasulphide.

Table 10 shows effectiveness of the additive compound comprising mixture(A+C) of present invention, with molar ration of 1:1 of High ReactivePolyisobutylene and Phosphorus Pentasulphide.

Discussion about Very High Effectiveness of Mixture (A+B), that is,Additive Compound of Present Invention, in Naphthenic Acid CorrosionInhibition

-   -   a) Referring to Table 1, effective active dosage of compound A        (molar ratio 1:1) of 300 ppm and 325 ppm were required to        achieve corrosion inhibition efficiency of 95.75% and 99.67%        respectively.    -   b) Referring to Table 2, effective active dosage of compound A        (molar ratio 1:0.5) of 250 ppm was required to achieve corrosion        inhibition efficiency of 75.48%.    -   c) Referring to Table 3, effective active dosage of compound A,        (molar ratio 1:0.25) of 500 ppm and 750 ppm were required to        achieve corrosion inhibition efficiency of 83.81% and 97.72%        respectively.    -   d) Referring to Table 4, effective active dosage of compound A,        with normal polyisobutylene (molar ratio 1:0.35) of 300 ppm gave        corrosion inhibition efficiency of only 54.39%.    -   e) Referring to Table 5, effective active dosage of compound B,        of 100 ppm gave corrosion inhibition efficiency of only 83:97%.    -   f) In contract, referring to Table 6, total effective active        dosage of mixture (A+B) of 150 ppm (75 ppm of A and 75 ppm of B)        and 150 ppm (90% of A and 60 ppm of B) gave corrosion inhibition        efficiency of 97.49% and 99.20% respectively.

This clearly shows the inventiveness of the mixture (A+B) of presentinvention, as very high corrosion inhibition efficiency of about 97% and99% are achieved with very low total effective active dosages themixture (A+B), that is, 150 ppm. This will effect tremendous savings dueto very low dosages of mixture.

Discussion about Very High Effectiveness of Mixture (A+C), that isAdditive Compound of Present Invention, in Naphthenic Acid CorrosionInhibition.

Referring to Table 9, effective active dosage of compound C, of 120 ppmand 150 ppm gave corrosion inhibition efficiency of 76.05% and 98.18%.

In contrast with results presented in Table 1 to 9, as discussed above,total effective active dosages of mixture (A+C) of present invention of200 ppm (140 ppm of A and 60 ppm of C) gave corrosion inhibitionefficiency of 99.54%. This leads to large savings, when it is noted thatcompound C is very expensive as compared to compound A.

Thus it is seen from the earlier discussion that the additive compoundsformed by two separate mixtures, (compound A+compound B) and (compoundA+compound C) of present invention used for corrosion-inhibition havethe following important distinguishing feature, as compared to the priorart.

The inventor of the present invention, after extensive experimentation,has surprisingly found that the two additive combination compounds, eachused by the inventor, as additive that is, two combination compoundsformed by two separate mixtures, (compound A+compound B) and (compoundA+compound C) are both highly effective in high temperature corrosioninhibition, as shown by the experimental results given in Tables 1 to11.

The prior-art does not teach or suggest use of mixture (A+B) or mixture(A+C) in naphthenic acid corrosion inhibition or sulphur corrosioninhibition or any corrosion inhibition, in general.

In view of the details given in foregoing description of the presentinvention, it will be apparent to a person skilled in the art that thepresent invention basically comprises the following items:

Item 1

A high temperature naphthenic acid corrosion inhibiting compositioncomprising a chemical mixture of corrosion inhibiting amount of anolefin Phosphorus sulphur compound A with corrosion inhibiting amount ofany organophosphorus compound selected from the group consisting ofcompound B, compound C and compound D; wherein said olefin Phosphorussulphur compound A, is produced by reacting said olefin with Phosphoruspentasulphide in presence of catalytic amount of sulphur, capablyforming a reaction mixture, with molar ratio of said olefin to saidPhosphorus pentasulphide being between 1:0.05 to 1:1.5, preferably being1:1; wherein said compound B is a phosphate ester of the formula

wherein R₁ and R₂ are each independently selected from the groupconsisting of hydrogen and moieties having from one to thirty carbonatoms, and R₃ is a moiety having from one to thirty carbon items; andwherein said compound C is an aryl containing phosphite compoundexcluding nitrogen having a structure selected from the group consistingof

wherein R₁, R₂ and R₃ are C₆ to C₁₂ aryl or alkyl and at least one Rgroup is an aryl radical; and wherein said compound D is a phosphonate.

Item 2

A composition, as described in item 1, wherein said olefin ispolyisobutylene, which is either high reactive or normal.

Item 3

A composition, as described in item 1 and 2, wherein said olefinPhosphorus sulphur compound is arrived at, by stirring and heating saidreaction mixture of item 1, to 160° C. under nitrogen gas purging,maintaining said reaction mixture between 160° C. to 180° C. for aperiod of 1 hour to 2 hours, raising temperature of said reactionmixture to from 185° C. to 250° C., preferably from 190° C. to 230° C.,more preferably from 210° C. to 225° C. and maintaining said reactionmixture with raised temperature for 1 to 24 hours, preferably for 6 to10 hours, cooling the reaction mass to 100° C. and purging nitrogen gasinto reaction vessel to drive out the hydrogen sulphide gas, therebyresulting into said composition.

Item 4

A composition according to item 1, 2 or 3 wherein said olefin is anoptionally substituted hydrocarbon group.

Item 5

A composition according to any one of the preceding items wherein saidolefin is an optionally substituted alkyl or alkenyl group.

Item 6

A composition according to any one of the preceding items wherein saidolefin is an optionally substituted branched alkyl or alkenyl group.

Item 7

A composition according to any one of the preceding items wherein saidolefin has between 10 and 1000 carbon atoms.

Item 8

A composition according to any one of the preceding items wherein saidolefin has between 4 and 200 carbon atoms.

Item 9

A composition according to any one of the preceding items wherein saidolefin has a molecular weight of from 200 to 10,000.

Item 10

A composition according to any one of the preceding items wherein saidolefin has a molecular weight of approximately 200 to approximately1300.

Item 11

A composition, comprising said mixture of compound A and compound B ofitem 1 and 14, wherein said phosphate ester B is selected from groupconsisting of phosphate, diphosphate, triphosphate, and tributylphosphate, preferably tributyl phosphate.

Item 12

A composition, as described in item 1, wherein said aryl containingphosphite compound C is selected from the group consisting of triphenylphosphite, diphenyl phosphite, diphenyl isodecyl phosphite, diphenylisooctyl phosphite, di-isodecyl phenyl phosphite and mixtures thereof,preferably di-isodecyl phenyl phosphite.

Item 13

A composition, as described in item 12, wherein said tributyl phosphateis of a type which is commercially available.

Item 14

A composition, as described in item 14, wherein said di-isodecyl phenylphosphite is of a type which is commercially available.

Item 15

A composition, as described in items 1, 11 and 13, wherein the amount ofsaid mixture of compound A and compound B, which should be added tocrude oil for high temperature naphthenic acid corrosion inhibition, isfrom about 1 ppm to about 5000 ppm, preferably from about 1 ppm to about300 ppm.

Item 16

A composition, as described in item 15, wherein the ratio of compound Ato compound B, by weight, is from about 0.1:2 to about 2:0.1.

Item 17

A composition, as described in items 1, 12 and 14, wherein the amount ofsaid mixture of compound A and compound C, which should be added tocrude oil for high temperature naphthenic acid corrosion inhibition, isfrom about 1 ppm to about 5000 ppm, preferably from about 1 ppm to about300 ppm.

Item 18

A composition, as described in item 17 wherein the ratio of compound Ato compound C, by weight, is from about 0.1:2 to about 2:0.1.

Item 19

A composition, as described in item 1, wherein the amount of mixture ofcompound A and compound D, which should be added to the crude oil forhigh temperature naphthenic acid corrosion inhibition, is from about 1ppm to about 5000 ppm, preferably from about 1 ppm to 300 ppm.

Item 20

A composition, as described in item 19, wherein the ratio of compound Ato compound D, by weight, is from about 0.1:2 to about 2:0.1.

Item 21

A process for high temperature naphthenic acid corrosion inhibitionand/or high temperature sulphur corrosion inhibition of metallicsurfaces of any of the hydrocarbon, processing units, with saidprocessing units comprising distillation columns, strippers, trays, pumparound piping and related equipments, using inhibitor combinationcompound such as, any mixture from three mixtures, such as, a mixture oftwo compounds A and B of item 1, 2, 11 and 13, or a mixture of twocompounds A and C of items 1, 2, 12 and 14, and a mixture of twocompounds A and D of items 1, 2, 19 and 20, comprising the steps of:

-   -   a. heating the hydrocarbon containing naphthenic acid and/or        sulphur compounds, to vapourize a portion of said hydrocarbon;    -   b. condensing a portion of the hydrocarbon vapours, passing        through said hydrocarbon processing unit, to produce a condensed        distillate;    -   c. adding to said distillate, before said condensed distillate        is returned to said hydrocarbon processing unit or collected as        a product, from about 1 ppm to about 5000 ppm, preferably from        about 1 ppm to 300 ppm of said inhibitor combination compound        such as, any mixture from three mixtures, such as, said mixture        of two compounds A and B of item 1, 2, 11 and 13, or said        mixture of two compounds A and C of items 1, 2, 12 and 14, and        said mixture of two compounds A and D of items 1, 2, 19 and 20,        wherein ratio by weight of A to B is from about 0.1:2 to about        2:0.1 and ratio of A to C is from about 0.1:2 to about 2:0.1.        and ratio by weight of A to D is from about 0.1:2 to about        2:0.1;    -   d. allowing said condensed distillate containing said inhibitor        combination compound such as, any mixture from three mixtures,        such as, said mixture of two compounds A and B of item 1, 2, 11        and 13, or said mixture of two compounds A and C of items 1, 2,        12 and 14, and said mixture of two compounds A and D of items 1,        2, 19 and 20, to contact said metallic surfaces of said        hydrocarbon processing unit, to form a protective film on said        surfaces whereby each surface is inhibited against corrosion;        and    -   e. allowing said condensed distillate to return to said        hydrocarbon processing unit, or to be collected as said product.

Although the invention has been described with reference to certainpreferred embodiments, the invention is not meant to be limited to thosepreferred embodiments. Alterations to the preferred embodimentsdescribed are possible without departing from the spirit of theinvention. However, the process and composition described above areintended to be illustrative only, and the novel characteristics of theinvention may be incorporated in other forms without departing from thescope of the invention.

1. A high temperature naphthenic acid corrosion inhibiting compositioncomprising a chemical mixture of corrosion inhibiting amount of anolefin Phosphorus sulphur compound A with corrosion inhibiting amount ofany organophosphorus compound selected from the group consisting ofcompound B, compound C and compound D; wherein said olefin Phosphorussulphur compound A, is produced by reacting said olefin with Phosphoruspentasulphide in presence of catalytic amount of sulphur, capablyforming a reaction mixture, with molar ratio of said olefin to saidPhosphorus pentasulphide being between 1:0.05 to 1:1.5, preferably being1:1; wherein said compound B is a phosphate ester of the formula

wherein R₁ and R₂ are each independently selected from the groupconsisting of hydrogen and moieties having from one to thirty carbonatoms, and R₃ is a moiety having from one to thirty carbon atoms; andwherein said compound C is an aryl containing phosphite compoundexcluding nitrogen having a structure selected from the group consistingof

wherein R₁, R₂ and R₃ are C₆ to C₁₂ aryl or alkyl and at least one Rgroup is an aryl radical; and wherein said compound D is a phosphonate.2. A composition of claim 1, wherein said olefin is polyisobutylene,which is either high reactive or normal.
 3. A composition of claim 2,wherein said olefin Phosphorus sulphur compound is arrived at, bystirring and heating said reaction mixture of claim 1, to 160° C. undernitrogen gas purging, maintaining said reaction mixture between 160° C.to 180° C. for a period of 1 hour to 2 hours, raising temperature ofsaid reaction mixture to from 185° C. to 250° C., preferably from 190°C. to 230° C., more preferably from 210° C. to 225° C. and maintainingsaid reaction mixture with raised temperature for 1 to 24 hours,preferably for 6 to 10 hours, cooling the reaction mass to 100° C. andpurging nitrogen gas into reaction vessel to drive out the hydrogensulphide gas, thereby resulting into said composition.
 4. A compositionof claim 1, wherein said olefin is an optionally substituted hydrocarbongroup.
 5. A composition of claim 4, wherein said olefin is an optionallysubstituted alkyl or alkenyl group.
 6. A composition of claim 5, whereinsaid olefin is an optionally substituted branched alkyl or alkenylgroup.
 7. A composition claim 1, wherein said olefin has between 10 and1000 carbon atoms.
 8. A composition of claim 1, wherein said olefin hasbetween 4 and 200 carbon atoms.
 9. A composition of claim 1, whereinsaid olefin has a molecular weight of from 200 to 10,000.
 10. Acomposition of claim 9, wherein said olefin has a molecular weight ofapproximately 200 to approximately
 1300. 11. A composition, comprisingsaid mixture of compound A and compound B of claim 1, wherein saidphosphate ester B is selected from group consisting of phosphate,diphosphate, triphosphate, and tributyl phosphate, preferably tributylphosphate.
 12. A composition of claim 1, wherein said aryl containingphosphite compound C is selected from the group consisting of triphenylphosphite, diphenyl phosphite, diphenyl isodecyl phosphite, diphenylisooctyl phosphite, di-isodecyl phenyl phosphite and mixtures thereof,preferably di-isodecyl phenyl phosphite.
 13. A composition of claim 1,further comprising tributyl phosphate wherein said tributyl phosphate isof a type which is commercially available.
 14. A composition of claim12, wherein said di-isodecyl phenyl phosphite is of a type which iscommercially available.
 15. A composition of claim 1, wherein the amountof said mixture of compound A and compound B, which should be added tocrude oil for high temperature naphthenic acid corrosion inhibition, isfrom about 1 ppm to about 5000 ppm, preferably from about 1 ppm to about300 ppm.
 16. A composition of claim 15, wherein the ratio of compound Ato compound B, by weight, is from about 0.1:2 to about 2:0.1.
 17. Acomposition of claim 1, wherein the amount of said mixture of compound Aand compound C, which should be added to crude oil for high temperaturenaphthenic acid corrosion inhibition, is from about 1 ppm to about 5000ppm, preferably from about 1 ppm to about 300 ppm.
 18. A composition ofclaim 17 wherein the ratio of compound A to compound C, by weight, isfrom about 0.1:2 to about 2:0.1.
 19. A composition of claim 1, whereinthe amount of mixture of compound A and compound D, which should beadded to the crude oil for high temperature naphthenic acid corrosioninhibition, is from about 1 ppm to about 5000 ppm, preferably from about1 ppm to 300 ppm.
 20. A composition of claim 19, wherein the ratio ofcompound A to compound D, by weight, is from about 0.1:2 to about 2:0.1.21. A process for high temperature naphthenic acid corrosion inhibitionof metallic surfaces of any of the hydrocarbon processing unitscomprising distillation columns, strippers, trays, pump around pipingand related equipments, using high temperature naphthenic acid corrosioninhibiting composition comprising a chemical mixture of corrosioninhibiting amount of an olefin Phosphorus sulphur compound A withcorrosion inhibiting amount of any organophosphorus compound selectedfrom the group consisting of compound B, compound C and compound D ofclaim 1, comprising the steps of: a. heating the hydrocarbon containingnaphthenic acid sulphur compounds, to vapourize a portion of saidhydrocarbon; b. condensing a portion of the hydrocarbon vapours, passingthrough said hydrocarbon processing unit, to produce a condenseddistillate; c. adding to said distillate, before said condenseddistillate is returned to said hydrocarbon processing unit or collectedas a product, from about 1 ppm to about 5000 ppm, preferably from about1 ppm to 300 ppm of said high temperature naphthenic acid corrosioninhibiting composition, wherein ratio by weight of said compound A tosaid compound B is from about 0.1:2 to about 2:0.1 and ratio of saidcompound A to said compound C is from about 0.1:2 to about 2:0.1, andratio by weight of said compound A to said compound D is from about0.1:2 to about 2:0.1; d. allowing said condensed distillate containingsaid high temperature naphthenic acid corrosion inhibiting compositionto contact said metallic surfaces of said hydrocarbon processing unit,to form a protective film on said surfaces whereby each surface isinhibited against corrosion; and e. allowing said condensed distillateto return to said hydrocarbon processing unit, or to be collected assaid product.
 22. (canceled)
 23. (canceled)
 24. A process as claimed inclaim 21, wherein said olefin is polyisobutylene, which is either highreactive or normal.
 25. A process according to claim 21, wherein saidolefin is an optionally substituted hydrocarbon group, preferably anoptionally substituted alkyl or alkenyl group, more preferably anoptionally substituted branched alkyl or alkenyl group.
 26. A processaccording to claim 21, wherein said olefin has between 4 and 1000 carbonatoms.
 27. A process according to claim 21, wherein said olefin has amolecular weight of from 200 to 10,000.
 28. A process as claimed inclaim 21, wherein said phosphate ester B is selected from groupconsisting of phosphate, diphosphate, triphosphate, and tributylphosphate, preferably tributyl phosphate.
 29. A process as claimed inclaim 21, wherein said high temperature naphthenic acid corrosioninhibiting composition further comprises tributyl phosphate wherein saidtributyl phosphate is of a type which is commercially available.
 30. Aprocess as claimed in claim 21, wherein said aryl containing phosphitecompound C is selected from the group consisting of triphenyl phosphite,diphenyl phosphite, diphenyl isodecyl phosphite, diphenyl isooctylphosphite, di-isodecyl phenyl phosphite and mixtures thereof, preferablydi-isodecyl phenyl phosphite.
 31. A process as claimed in claim 30,wherein said di-isodecyl phenyl phosphite is of a type which iscommercially available.
 32. A process as claimed in claim 21, whereinsaid hydrocarbon containing naphthenic acid compound also containssulphur compounds.